1. Field of the Invention
The present invention relates to centerbodies utilized in multiple annular gas turbine engine combustors to separate concentrically disposed annular combustion zones thereof and, more particularly, to centerbodies of multiple annular gas turbine engine combustors having specific geometric configurations to reduce thermal stresses thereon.
2. Description of Related Art
Centerbodies are well known in the combustor art of gas turbine engines for separating or segregating concentric combustion zones of multiple annular combustors, as seen in U.S. Pats. Nos. 5,197,278 and 5,289,687. In particular, such centerbodies are useful for isolating the annular combustion zone acting as the pilot stage, which ensures combustion stability at various operating points and allows dilution air to be directed into the pilot stage reaction zone. In the arrangements depicted in these patents, the centerbody is connected at its upstream end directly to the dome plate defining the combustion zones.
A second arrangement involves the incorporation of one or more centerbodies with a heat shield for a multiple annular combustor, as disclosed in U.S. Pat. No. 5,323,604. Such heat shields are utilized to protect the dome portion thereof against extreme heat caused by the flame within the combustion chamber. Since multiple annular combustors are staged according to a predetermined scheme, such as disclosed in U.S. Pat. No. 5,303,542, with respect to a triple annular combustor, the centerbodies therein are used to assist in ensuring only the desired combustion regions are lit as appropriate. This is extremely important in the overall goal of reducing emissions produced by the combustor. The centerbodies of the outer and inner heat shields may also be utilized to protect the outer and inner liners, respectively, as shown in U.S. Pat. No. 5,323,604.
It has been found that staged burner operation of a multiple annular combustor causes thermal gradients across a centerbody, which results in thermal stresses being imposed thereon that reduce its useful life. It will be undertood that such thermal gradients have an axial component and a circumferential component. To prevent the thermal stresses from reaching a level having a catastrophic effect on the centerbody, cooling air flow has generally been employed around the centerbody to reduce the changes in temperature thereacross. However, this measure is not desirable since the cooling air supply is limited by engine thermodynamics and emissions. Another measure utilized is to increase the thermal barrier coating on such a centerbody to counteract the thermal effects thereon, but this adds cost to the engine part and the thermal barrier coating loses effectiveness over time.
Accordingly, it would be desirable for a centerbody design to be developed, either separately or in conjunction with a combustor heat shield, which minimizes the effect of circumferential thermal gradients and resultant thermal stresses thereon to increase the cyclic life and durability of the centerbody without the disadvantages associated with current measures.